1. Field of the Invention
The present invention relates to a retractable needle safety syringe in which the needle may be withdrawn into the barrel of the syringe after use. More particularly the invention relates to a retractable needle syringe wherein the plunger need not be connected to the needle or its carrier for the retraction. Most particularly the invention relates to a retractable needle syringe wherein the needle carrier is spring loaded so that it may be automatically retracted into the syringe barrel after use.
2. Related Art
Due to the recent advent of the AIDS virus, which may be contracted by contaminated hypodermic syringes, there have been several retractable needle hypodermic syringes invented and patented. The retraction of the needle into the barrel of the syringe after use reduces the risk of "needle prick", or the accidental pricking of the person giving the injection after the syringe has been used.
Some of the recently patented retractable needle syringes include U.S. Pat. Nos. 4,692,156 (Haller); 4,675,005 (DeLuccia); 4,747,830 (Gloyer, et al); 4,790,822 and 4,950,251. All of the syringes disclosed include a hypodermic needle mounted on a carrier which is slidable in the barrel. The plunger is locked to this carrier after the injection has been given and is withdrawn up into the barrel by withdrawal of the plunger. The simplest mechanism for locking the plunger to the carrier is disclosed as a projection on the lower end of the plunger which engages through an opening in the upper end of the carrier.
One disadvantage of the above syringes is that the locking mechanism takes up some space in the barrel of the syringe and may prevent all of the measured liquid from being ejected by the plunger. This problem is exacerbated in the very small syringes such as the 1 cc tuberculin type. The liquid left in the barrel may be a substantial portion of the measured dose. In addition the narrowness of the barrel of the 1 cc syringe makes it difficult to design a needle carrier and locking that will fit in the barrel without enlarging the diameter so much as to make the calibration useless.
Venturini in U.S. Pat. No. 5,112,316 discloses a syringe similar to the retractable needle syringes described above except Venturini adds a spring outside the upper end of the syringe between the finger flange on the top of the barrel and the bottom surface of a projection at the top of the plunger to retract the plunger into the barrel after it has been locked onto the needle carrier. Venturini suffers the same draw backs because the plunger must still be locked to the needle carrier.